AE CS6 Alpha cutout or knockout in a 3D scene?

I have a 3D reasonably complex scene. It's setup with motion blur and DOF too. I'd like to cutout a portion of one layer in that scene so that when I bring the video into Premiere Pro, I can layer it over the top of a video and have the video show through.

What I'm after is some kind of effect or plugin or proceedure that allows a cutout in a layer but that also cuts out layers behind/beneath it in 3D.

I guess I could pre-compose the entire scene and create a track matte but as there's a lot of DOF blurring and motion blur, not sure if that would work very well?